Mask generation for part of an image

[joelshort]

I'm working on a mosaic image that has two main galaxies in the image.  I'd like to apply slightly different HDRMultiscaleTransform iterations on the separate galaxies.  Is there a way to create a mask that just applies to one galaxy and not the other?

[RickS]

Create a mask for both galaxies, draw a preview around one of them and use the SubstituteWithPreview script.  The mask will be the source image and you'll need to create a black image the same size as your mask as the target image (just clone the mask image and use PixelMath with "0" as the RGB/K expression.)

Cheers,
Rick.

[joelshort]

Thanks Rick, that worked great.